Potassium deficiency? close to harvest

[RUBY]

Hi, am growing critical kush for the 1st time and it's been real slow. day 69 in flower and probably only 20% pistils turned so far. However have dropped temp and humidity right down after heat probs last time.
Over last couple of days some of the upper leaves look like they may have developed a potassium deficiency. Was planning another few days on nutes before switching to flush for 7-14 days but its going to be hard to tell if they'll be ready to switch to flush. Any advice much appreciated.
Also am using terpinator for the 1st time. Jury is out on this at the mo but have noticed system has developed a 'sludge' problem that its never had before. (will try Ataclean) has anyone else had this with terpinator?

[Green75]

We need a pic please...
69 days....gotta see it

[Pankace]

Pics! Day 69 should be about harvest time. The deficiency could just be the leaves naturally turning from being so close to harvest.

[ZigZag]

Would tend to agree with Pankace...my leaves almost always start to turn yellow the last two weeks or so...I usually start the flush about 7-10 days before harvest in soil and 5-7 days before in coco. But in hydro it seems you could wait until the last 3-5 days or so. On my last harvest I began my flush probably too early_ I was growing some OG this last time and some of the plants flowering time ended up being longer than I'd anticipated....up to 3 weeks longer than the first ones! As a result I started the flush on some of them too early_ those plants could have used some more nutrients for longer. Nest time I'm going to wait until I have at 75% brown pistils with cloudy trichomes , maybe even wait until there are about 10-20% amber trichomes_before I start the flush a week before harvest, and do this on a plant by plant basis. That way I should get as much growth as possible and a good flush as well. I hope!

[RUBY]

think I sussed it. Ran out of canna boost last week, thought they'd manage the last week or so without. Obviously not! Not sure whether to reintroduce now for last week or so on nutes. Any advice appreciated!